A picked-up image by a camera is made unclear by floating objects in the air such as haze, fog, and mist. In the following explanation, haze represents haze, fog, mist, and the like.
Therefore, there has been proposed image processing for haze removal for removing the influence of haze from picked-up image data. The image processing is proposed in, for example, Japanese Patent Application Laid-open No. 2013-58202, Japanese Patent Application Laid-open No. 2012-221237, Japanese Patent Application Laid-open No. 2011-3048, and Japanese Patent Application Laid-open No. 2004-222231.
As one image processing for haze removal, there is processing based on prior information called dark channel prior. The processing is based on the premise that a picture in which an intensity value of at least one color channel of RGB values is very small (in general, a dark gradation value close to 0) is present in statistical values obtained from an outdoor image group without haze, that is, a large number of non-sky local regions of outdoor images without haze. Therefore, if a value of a dark color channel in a picked-up image is low, haze is thin and the permeability of the air is high. On the other hand, if the value of the dark color channel in the picked-up image is high, the haze is thick and the permeability of the air is low. With a haze removal model generated using the dark channel prior, it is possible to not only directly estimate the concentration of the haze but also generate a high-quality image (referred to as haze removed image) after the disturbance of the haze is removed from an image in which haze is present (hereinafter referred to as image with haze). The image processing for haze removal is described in Japanese Patent Application Laid-open No. 2013-58202.